1. Field of the Invention
The present invention relates to a wiper arm and a wiper device for wiping a windshield of a vehicle.
2. Description of the Related Art
A wiper device for wiping a windshield of a vehicle is generally equipped with two sets of wiper arms and wiper blades.
The wiper arm has an arm-head fixed to a pivot at an end thereof and rotatably connected to a retainer by a spindle at the other end thereof. A spring member is fixed between the arm-head and the retainer to press the retainer against the windshield surface to be wiped. An arm piece is fixed to the retainer at an end thereof. The arm piece has a generally U-shaped holder to hold the wiper blade.
The wiper blade is composed of a rubber blade and a plurality of holder levers for holding the rubber blade.
When the wiper device operates, the wiper arm and the wiper blade swings to wipe off rain drops on the windshield.
As shown in FIG. 12, retainer 82 of such a wiper arm has side walls forming a U-shape channel, and an open side thereof which faces the windshield surface. If retainer 82 is put in air flow S while the vehicle runs at a high speed, big noises or soughs may be generated. When retainer 82 is exposed to such high speed air flow S, Karlman's vortexes are generated at the rear of side wall 84 of retainer 82 located at the upstream side of the air flow S and also high frequency vibration called cavity tones or edge tones is generated as the vortexes hit the other side wall 86 located at the down stream. The cavity tones resonate inside the retainer 82 thereby generating big noises.
In order to prevent such big noises, JP-U-59-66652 proposes a retainer having a notch at the side wall located at the downstream side of the air flow. If high speed air flow hits the retainer to form vortexes, the vortex can not always hit the side wall located at the down stream side of the air flow. However, this structure can not eliminate the vortexes and, therefore, can not prevent the cavity tones completely.